Knocking (also called knock, detonation, spark knock, pinging or pinking) in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.
The fuel-air charge is meant to be ignited by the spark plug only, and at a precise time in the piston's stroke cycle. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
Knocking should not be confused with pre-ignition. Wikipedia, Engine Knocking
Schauberger
With explosions vorticity (turbulence) always occurs, resulting in a reduction in the velocity of the through-flowing substance, leading in turn to cavitation, viz. the corrosion on [a] ship propeller or pressure screws in turbines. In particular when snow meltwater or glacier water is centrifugated. In such cases radar-like retroactive reactions takes place, which as detonating events, have a shattering effect. The detonation velocity can be a thousand times greater than the normal combustion velocity, which explains, for example, why the resistance to motion increases by the square in all explosion and expansion machines, which also increases by the square of the velocity of an increase in heat. It therefore acts to impede motion. [The Energy Evolution - Harnessing Free Energy from Nature, Explosion and Implosion - Expansion and Impansion]
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